The prior art is replete with various transmission designs for off-highway implements such as tractors and the like. Such transmission designs typically include a casing that houses a plurality of selectively operable gear meshes that transfer rotary power and develop different turning speed ratios between generally parallel shafts rotatably mounted within the transmission. A series of clutch assemblies operably and selectively couple various gear meshes to each other to operate the implement in a selected condition. Some off-highway implement transmissions have a multi-speed transmission section coupled to a multi-range transmission section to offer a multitude of gear ratios capable of developing various ground speeds for the off-highway implement.
During field operation, the transmission of the implement is typically conditioned such that the engine is permitted to operate or run at a specified and generally constant speed thus developing a constant ground speed for the implement. Although the clutch assemblies can be independently conditioned such that the selected gear meshes, in combination, define as many as twelve different ground speeds for the implement, the slowest ground speeds for the implement may still be inadequate for some field operations. For example, it is often desirable to condition the transmission in a super slow speed condition such that the ground speed of the implement is such that it allows workers to perform any special field or gardening operations requiring a slow moving unit, i.e., broccoli harvesting, planting of tomato or other plants, and etc.
Another factor of significance regarding transmission designs is that some off-highway or agricultural implement transmissions have an excessive axial length. Accordingly, it is difficult to fit a transmission having both speed and range transmission sections into only limited space constraints that are typically available with an agricultural implement. Reducing the size of the transmission normally reduces the number of gear ratio combination that are achievable, thus, further complicating the needs mentioned above.
As will be appreciated by those skilled in the transmission art, off-highway implement transmissions often include at least one elongated shaft assembly on which multiple helical gears are mounted in axially spaced relation relative to each other. The elongated shaft assembly is rotatably journalled in the transmission casing or housing by a series of anti-friction bearings. In those transmission designs that utilize three bearings disposed in axially spaced relation along the length of a one-piece shaft, the bearings have been known to not statically support the load imparted thereto by the turning shaft thus offering a statically indeterminate structure and, thus, unpredictable performance.
In some transmission designs, the shaft assembly includes two axially aligned shafts that are interconnected to each other to act as a solid and elongated shaft. Normally, each shaft of the shaft assembly is supported in the casing or housing by a set of two bearings. To address the axial loading applied to the shaft assembly by intermeshing helical gears during operation of the transmission, each bearing set includes two tapered or conical roller bearings; with one bearing being provided toward opposite ends of each shaft of each shaft assembly. Thus, there are as many as four bearings associated with each elongated shaft assembly. As is well known in the art, each bearing set requires adjustment to compensate for clearances inherent between bearing components Shaft end play will be determined by the clearances set for each bearing. Accordingly, in those elongated transmission shaft assemblies that embody two axially aligned and interconnected shafts, two separate adjustments need to be made to each shaft assembly to compensate for axial loading imparted thereto through the intermeshing gear meshes.
Accordingly, there is both a need and a desire for a transmission assembly for an off-highway implement that offers the necessary gear ratio combinations which allow both an extremely slow ground speed coupled with a constant engine speed and a relatively compact design. Furthermore, there is a need and desire for a transmission assembly that embodies a simplified form of adjustment for the bearings that journal axially elongated shafts used in the transmission assembly.